I'd be interested at prompting others about this; those who have downloaded SilverStripe and got it going on their webhosts. We run our own boxes, which means we run whatever Debian (Etch) is up to, currently 5.2.0.
http://packages.debian.org/testing/net/libapache2-mod-php5
You have inspired me to contact some NZ hosts, given this was a topic on the NZ PHP Group a few weeks back, and I didn't see anyone shout out and say a domestic webfarm style (under $30/month) business provided PHP5 hosting. It seems to something that premium hosting companies (e.g. $100+ a month) provide (there are a few of these, including ourselves), from what I can tell.
I see http://www.a2hosting.com (international) being mentioned a bit, and this provides PHP 5.2.1 currently, as well as subversion, ruby on rails etc, so these guys are obviously providing a decent service rather than lazing about with draconian server software versions.